Color stable red-emitting phosphors

ABSTRACT

A process for synthesizing a Mn 4+  doped phosphor includes contacting a precursor of formula I, 
                         
at an elevated temperature with a fluorine-containing oxidizing agent in gaseous form to form the color stable Mn 4+  doped phosphor;
         wherein
           A is Li, Na, K, Rb, Cs, or a combination thereof;   M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Hf, Y, La, Nb, Ta, Bi, Gd, or a combination thereof;   x is the absolute value of the charge of the [MF y ] ion;   y is 5, 6 or 7; and   amount of Mn ranges from about 0.9 wt % to about 4 wt %, based on total weight.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of and claims priority fromU.S. application Ser. No. 14/302,823, filed Jun. 12, 2014, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND

Red-emitting phosphors based on complex fluoride materials activated byMn⁴⁺, such as those described in U.S. Pat. No. 7,358,542, U.S. Pat. No.7,497,973, and U.S. Pat. No. 7,648,649, can be utilized in combinationwith yellow/green emitting phosphors such as YAG:Ce or other garnetcompositions to achieve warm white light (CCTs<5000 K on the blackbodylocus, color rendering index (CRI)>80) from a blue LED, equivalent tothat produced by current fluorescent, incandescent and halogen lamps.These materials absorb blue light strongly and efficiently emit betweenabout 610-635 nm with little deep red/NIR emission. Therefore, luminousefficacy is maximized compared to red phosphors that have significantemission in the deeper red where eye sensitivity is poor. Quantumefficiency can exceed 85% under blue (440-460 nm) excitation.

While the efficacy and CRI of lighting systems using Mn⁴⁺ doped fluoridehosts can be quite high, one potential limitation is theirsusceptibility to degradation under high temperature and humidity (HTHH)conditions and high light fluxes. US 2014/0264418 describes processesthat can increase color stability of Mn⁴⁺ doped complex fluoridematerials containing up to 1.5 wt % manganese. However, improved colorstability and other properties important for use with LEDs is desirablefor materials containing higher levels of manganese.

BRIEF DESCRIPTION

Briefly, in one aspect, the present invention relates to a process forsynthesizing a Mn⁴⁺ doped phosphor. A precursor of formula I iscontacted with a fluorine-containing oxidizing agent in gaseous form atan elevated temperature to form the Mn⁴⁺ doped phosphor

wherein

-   -   A is Li, Na, K, Rb, Cs, or a combination thereof;    -   M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Hf, Y, La, Nb, Ta, Bi,        Gd, or a combination thereof;    -   x is the absolute value of the charge of the [MF_(y)] ion;    -   y is 5, 6 or 7; and    -   an amount of Mn ranges from about 0.9 wt % to about 4 wt %,        based on total weight.

In another aspect, the present invention relates to color stable Mn⁴⁺doped phosphors of formula I.

In yet another aspect, the present invention relates to a lightingapparatus having a color temperature less than or equal to 4200° K, andincluding a red phosphor consisting of a color stable Mn⁴⁺ dopedphosphor of formula I.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic cross-sectional view of a lighting apparatus inaccordance with one embodiment of the invention;

FIG. 2 is a schematic cross-sectional view of a lighting apparatus inaccordance with another embodiment of the invention;

FIG. 3 is a schematic cross-sectional view of a lighting apparatus inaccordance with yet another embodiment of the invention;

FIG. 4 is a cutaway side perspective view of a lighting apparatus inaccordance with one embodiment of the invention;

FIG. 5 is a schematic perspective view of a surface-mounted device (SMD)backlight LED.

DETAILED DESCRIPTION

In the processes according to the present invention, a non-color stableprecursor to a color stable phosphor is annealed, or subjected to anelevated temperature, while in contact with an atmosphere containing afluorine-containing oxidizing agent. The precursor is a Mn⁴⁺ dopedcomplex fluoride material of formula I. In the context of the presentinvention, the term “complex fluoride material or phosphor”, means acoordination compound, containing at least one coordination center,surrounded by fluoride ions acting as ligands, and charge-compensated bycounter ions as necessary. In one example, K₂SiF₆:Mn⁴⁺, the coordinationcenter is Si and the counterion is K. Complex fluorides are occasionallywritten down as a combination of simple, binary fluorides but such arepresentation does not indicate the coordination number for the ligandsaround the coordination center. The square brackets (occasionallyomitted for simplicity) indicate that the complex ion they encompass isa new chemical species, different from the simple fluoride ion. Theactivator ion (Mn⁴⁺) also acts as a coordination center, substitutingpart of the centers of the host lattice, for example, Si. The hostlattice (including the counter ions) may further modify the excitationand emission properties of the activator ion.

The amount of manganese in the Mn⁴⁺ doped precursors may be as low asabout 0.9 wt % (about 3.5 mol %). The amount of manganese in the Mn⁴⁺doped precursors may be as high as about 3 wt % (about 12 mol %), andparticularly about 3.4 wt % (about 14 mol %), and more particularlyabout 4 wt % (about 16.5 mol %). Light emitting properties of theprecursors of formula I can be maintained or even improved at relativelyhigh levels of Mn by using the processes of the present invention.

In particular embodiments, the coordination center of the precursor,that is, M in formula I, is Si, Ge, Sn, Ti, Zr, or a combinationthereof. More particularly, the coordination center is Si, Ge, Ti, or acombination thereof, and the counterion, or A in formula I, is Na, K,Rb, Cs, or a combination thereof, and y is 6. Examples of precursors offormula I include K₂[SiF₆]:Mn⁴⁺, K₂[TiF₆]:Mn⁴⁺, K₂[SnF₆]:Mn⁴⁺,Cs₂[TiF₆]:Mn⁴⁺, Rb₂[TiF₆]:Mn⁴⁺, Cs₂[SiF₆]:Mn⁴⁺, Rb₂[SiF₆]:Mn⁴⁺,Na₂[TiF₆]:Mn⁴⁺, Na₂[ZrF₆]:Mn⁴⁺, K₃[ZrF₇]:Mn⁴⁺, K₃[BiF₆]:Mn⁴⁺,K₃[YF₆]:Mn⁴⁺, K₃[LaF₆]:Mn⁴⁺, K₃[GdF₆]:Mn⁴⁺, K₃[NbF₇]:Mn⁴⁺,K₃[TaF₇]:Mn⁴⁺. In particular embodiments, the precursor of formula I isK₂SiF₆:Mn⁴⁺.

The temperature at which the precursor is contacted with thefluorine-containing oxidizing agent is any temperature in the range fromabout 200° C. to about 700° C., particularly from about 350° C. to about600° C. during contact, and in some embodiments from about 500° C. toabout 600° C. The phosphor precursor is contacted with the oxidizingagent for a period of time sufficient to convert it to a color stablephosphor. Time and temperature are interrelated, and may be adjustedtogether, for example, increasing time while reducing temperature, orincreasing temperature while reducing time. In particular embodiments,the time is at least one hour, particularly for at least four hours,more particularly at least six hours, and most particularly at leasteight hours.

After holding at the elevated temperature for the desired period oftime, the temperature in the furnace may be reduced at a controlled ratewhile maintaining the oxidizing atmosphere for an initial coolingperiod. After the initial cooling period, the cooling rate may becontrolled at the same rate or a different rate, or may be uncontrolled.In some embodiments, the cooling rate is controlled at least until atemperature of 200° C. is reached. In other embodiments, the coolingrate is controlled at least until a temperature at which it is safe topurge the atmosphere is reached. For example, the temperature may bereduced to about 50° C. before a purge of the fluorine atmospherebegins.

Reducing the temperature at a controlled rate of ≦5° C. per minute mayyield a phosphor product having superior properties compared to reducingthe temperature at a rate of 10° C./minute. In various embodiments, therate may be controlled at ≦5° C. per minute, particularly at ≦3° C. perminute, more particularly at a rate of ≦1° C. per minute.

The period of time over which the temperature is reduced at thecontrolled rate is related to the contact temperature and cooling rate.For example, when the contact temperature is 540° C. and the coolingrate is 10° C./minute, the time period for controlling the cooling ratemay be less than one hour, after which the temperature may be allowed tofall to the purge or ambient temperature without external control. Whenthe contact temperature is 540° C. and the cooling rate is ≦5° C. perminute, then the cooling time may be less than two hours. When thecontact temperature is 540° C. and the cooling rate is ≦3° C. perminute, then the cooling time may be less than three hours. When thecontact temperature is 540° C. and the cooling rate is ≦1° C. perminute, then the cooling time is may be less than four hours. Forexample, the temperature may be reduced to about 200° C. with controlledcooling, then control may be discontinued. After the controlled coolingperiod, the temperature may fall at a higher or lower rate than theinitial controlled rate.

The fluorine-containing oxidizing agent may be F₂, HF, SF₆, BrF₅,NH₄HF₂, NH₄F, KF, AlF₃, SbF₅, ClF₃, BrF₃, KrF, XeF₂, XeF₄, NF₃, SiF₄,PbF₂, ZnF₂, SnF₂, CdF₂ or a combination thereof. In particularembodiments, the fluorine-containing oxidizing agent is F₂. The amountof oxidizing agent in the atmosphere may be varied to obtain the colorstable phosphor, particularly in conjunction with variation of time andtemperature. Where the fluorine-containing oxidizing agent is F₂, theatmosphere may include at least 0.5% F₂, although a lower concentrationmay be effective in some embodiments. In particular the atmosphere mayinclude at least 5% F₂ and more particularly at least 20% F₂. Theatmosphere may additionally include nitrogen, helium, neon, argon,krypton, xenon, in any combination with the fluorine-containingoxidizing agent. In particular embodiments, the atmosphere is composedof about 20% F₂ and about 80% nitrogen.

The manner of contacting the precursor with the fluorine-containingoxidizing agent is not critical and may be accomplished in any waysufficient to convert the precursor to a color stable phosphor havingthe desired properties. In some embodiments, the chamber containing theprecursor may be dosed and then sealed such that an overpressuredevelops as the chamber is heated, and in others, the fluorine andnitrogen mixture is flowed throughout the anneal process ensuring a moreuniform pressure. In some embodiments, an additional dose of thefluorine-containing oxidizing agent may be introduced after a period oftime.

In another aspect, the present invention relates to a process thatincludes contacting a precursor at an elevated temperature with afluorine-containing oxidizing agent in gaseous form to form the colorstable Mn⁴⁺ doped phosphor; the precursor is selected from the groupconsisting of

-   -   (A) A₂[MF₅]:Mn⁴⁺, where A is selected from Li, Na, K, Rb, Cs,        and combinations thereof; and where M is selected from Al, Ga,        In, and combinations thereof;    -   (B) A₃[MF₆]:Mn⁴⁺, where A is selected from Li, Na, K, Rb, Cs,        and combinations thereof; and where M is selected from Al, Ga,        In, and combinations thereof;    -   (C) Zn₂[MF₇]:Mn⁴⁺, where M is selected from Al, Ga, In, and        combinations thereof;    -   (D) A[In₂F₇]:Mn⁴⁺ where A is selected from Li, Na, K, Rb, Cs,        and combinations thereof;    -   (E) A₂[MF₆]:Mn⁴⁺, where A is selected from Li, Na, K, Rb, Cs,        and combinations thereof; and where M is selected from Ge, Si,        Sn, Ti, Zr, and combinations thereof;    -   (F) E[MF₆]:Mn⁴⁺, where E is selected from Mg, Ca, Sr, Ba, Zn,        and combinations thereof; and where M is selected from Ge, Si,        Sn, Ti, Zr, and combinations thereof;    -   (G) Ba_(0.65)Zr_(0.35)F_(2.70):Mn⁴⁺; and    -   (H) A₃[ZrF₇]:Mn⁴⁺ where A is selected from Li, Na, K, Rb, Cs,        and combinations thereof; and    -   the amount of Mn ranges from about 0.5 wt % to about 4 wt %,        based on total weight.

The amount of manganese in the Mn⁴⁺ doped precursors may be as low asabout 0.9 wt % (about 2.5 mol), and in some embodiments may be as low as1.5 wt % (about 6 mol %). The amount of manganese in the Mn⁴⁺ dopedprecursors may be as high as about 3 wt % (about 12 mol %), andparticularly about 3.4 wt % (about 14 mol %), and more particularlyabout 4 wt % (about 16.5 mol %). Time, temperature andfluorine-containing oxidizing agents for the process are describedabove.

Color stability and quantum efficiency of phosphors annealed in aprocess according to the present invention may be enhanced by treatingthe phosphor in particulate form with a saturated solution of acomposition of formula II

in aqueous hydrofluoric acid, as described in U.S. Pat. No. 8,252,613.The temperature at which the phosphor is contacted with the solutionranges from about 20° C. to about 50° C. The period of time required toproduce the color stable phosphor ranges from about one minute to aboutfive hours, particularly from about five minutes to about one hour.Concentration of hydrofluoric acid in the aqueous HF solutions rangesfrom about 20% w/w to about 70% w/w, particularly about 40% w/w to about70% w/w. Less concentrated solutions may result in lower yields of thephosphor.

Any numerical values recited herein include all values from the lowervalue to the upper value in increments of one unit provided that thereis a separation of at least 2 units between any lower value and anyhigher value. As an example, if it is stated that the amount of acomponent or a value of a process variable such as, for example,temperature, pressure, time and the like is, for example, from 1 to 90,preferably from 20 to 80, more preferably from 30 to 70, it is intendedthat values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. areexpressly enumerated in this specification. For values which are lessthan one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 asappropriate. These are only examples of what is specifically intendedand all possible combinations of numerical values between the lowestvalue and the highest value enumerated are to be considered to beexpressly stated in this application in a similar manner.

A lighting apparatus or light emitting assembly or lamp 10 according toone embodiment of the present invention is shown in FIG. 1. Lightingapparatus 10 includes a semiconductor radiation source, shown as lightemitting diode (LED) chip 12, and leads 14 electrically attached to theLED chip. The leads 14 may be thin wires supported by a thicker leadframe(s) 16 or the leads may be self supported electrodes and the leadframe may be omitted. The leads 14 provide current to LED chip 12 andthus cause it to emit radiation.

The lamp may include any semiconductor blue or UV light source that iscapable of producing white light when its emitted radiation is directedonto the phosphor. In one embodiment, the semiconductor light source isa blue emitting LED doped with various impurities. Thus, the LED maycomprise a semiconductor diode based on any suitable III-V, II-VI orIV-IV semiconductor layers and having an emission wavelength of about250 to 550 nm. In particular, the LED may contain at least onesemiconductor layer comprising GaN, ZnSe or SiC. For example, the LEDmay comprise a nitride compound semiconductor represented by the formulaIn_(i)Ga_(j)Al_(k)N (where 0≦i; 0≦j; 0≦k and I+j+k=1) having an emissionwavelength greater than about 250 nm and less than about 550 nm. Inparticular embodiments, the chip is a near-uv or blue emitting LEDhaving a peak emission wavelength from about 400 to about 500 nm. SuchLED semiconductors are known in the art. The radiation source isdescribed herein as an LED for convenience. However, as used herein, theterm is meant to encompass all semiconductor radiation sourcesincluding, e.g., semiconductor laser diodes. Further, although thegeneral discussion of the exemplary structures of the inventiondiscussed herein is directed toward inorganic LED based light sources,it should be understood that the LED chip may be replaced by anotherradiation source unless otherwise noted and that any reference tosemiconductor, semiconductor LED, or LED chip is merely representativeof any appropriate radiation source, including, but not limited to,organic light emitting diodes.

In lighting apparatus 10, phosphor composition 22 is radiationallycoupled to the LED chip 12. Radiationally coupled means that theelements are associated with each other so radiation from one istransmitted to the other. Phosphor composition 22 is deposited on theLED 12 by any appropriate method. For example, a water based suspensionof the phosphor(s) can be formed, and applied as a phosphor layer to theLED surface. In one such method, a silicone slurry in which the phosphorparticles are randomly suspended is placed around the LED. This methodis merely exemplary of possible positions of phosphor composition 22 andLED 12. Thus, phosphor composition 22 may be coated over or directly onthe light emitting surface of the LED chip 12 by coating and drying thephosphor suspension over the LED chip 12. In the case of asilicone-based suspension, the suspension is cured at an appropriatetemperature. Both the shell 18 and the encapsulant 20 should betransparent to allow white light 24 to be transmitted through thoseelements. Although not intended to be limiting, in some embodiments, themedian particle size of the phosphor composition ranges from about 1 toabout 50 microns, particularly from about 15 to about 35 microns.

In other embodiments, phosphor composition 22 is interspersed within theencapsulant material 20, instead of being formed directly on the LEDchip 12. The phosphor (in the form of a powder) may be interspersedwithin a single region of the encapsulant material 20 or throughout theentire volume of the encapsulant material. Blue light emitted by the LEDchip 12 mixes with the light emitted by phosphor composition 22, and themixed light appears as white light. If the phosphor is to beinterspersed within the material of encapsulant 20, then a phosphorpowder may be added to a polymer or silicone precursor, loaded aroundthe LED chip 12, and then the polymer precursor may be cured to solidifythe polymer or silicone material. Other known phosphor interspersionmethods may also be used, such as transfer loading.

In some embodiments, the encapsulant material 20 is a silicone matrixhaving an index of refraction R, and, in addition to phosphorcomposition 22, contains a diluent material having less than about 5%absorbance and index of refraction of R±0.1. The diluent material has anindex of refraction of ≦1.7, particularly ≦1.6, and more particularly≦1.5. In particular embodiments, the diluent material is of formula II,and has an index of refraction of about 1.4. Adding an opticallyinactive material to the phosphor/silicone mixture may produce a moregradual distribution of light flux through the phosphor/encapsulantmixture and can result in less damage to the phosphor. Suitablematerials for the diluent include fluoride compounds such as LiF, MgF₂,CaF₂, SrF₂, AlF₃, K₂NaAlF₆, KMgF₃, CaLiAlF₆, K₂LiAlF₆, and K₂SiF₆, whichhave index of refraction ranging from about 1.38 (AlF₃ and K₂NaAlF₆) toabout 1.43 (CaF₂), and polymers having index of refraction ranging fromabout 1.254 to about 1.7. Non-limiting examples of polymers suitable foruse as a diluent include polycarbonates, polyesters, nylons,polyetherimides, polyetherketones, and polymers derived from styrene,acrylate, methacrylate, vinyl, vinyl acetate, ethylene, propylene oxide,and ethylene oxide monomers, and copolymers thereof, includinghalogenated and unhalogenated derivatives. These polymer powders can bedirectly incorporated into silicone encapsulants before silicone curing.

In yet another embodiment, phosphor composition 22 is coated onto asurface of the shell 18, instead of being formed over the LED chip 12.The phosphor composition is preferably coated on the inside surface ofthe shell 18, although the phosphor may be coated on the outside surfaceof the shell, if desired. Phosphor composition 22 may be coated on theentire surface of the shell or only a top portion of the surface of theshell. The UV/blue light emitted by the LED chip 12 mixes with the lightemitted by phosphor composition 22, and the mixed light appears as whitelight. Of course, the phosphor may be located in any two or all threelocations or in any other suitable location, such as separately from theshell or integrated into the LED.

FIG. 2 illustrates a second structure of the system according to thepresent invention. Corresponding numbers from FIGS. 1-4 (e.g. 12 inFIGS. 1 and 112 in FIG. 2) relate to corresponding structures in each ofthe figures, unless otherwise stated. The structure of the embodiment ofFIG. 2 is similar to that of FIG. 1, except that the phosphorcomposition 122 is interspersed within the encapsulant material 120,instead of being formed directly on the LED chip 112. The phosphor (inthe form of a powder) may be interspersed within a single region of theencapsulant material or throughout the entire volume of the encapsulantmaterial. Radiation (indicated by arrow 126) emitted by the LED chip 112mixes with the light emitted by the phosphor 122, and the mixed lightappears as white light 124. If the phosphor is to be interspersed withinthe encapsulant material 120, then a phosphor powder may be added to apolymer precursor, and loaded around the LED chip 112. The polymer orsilicone precursor may then be cured to solidify the polymer orsilicone. Other known phosphor interspersion methods may also be used,such as transfer molding.

FIG. 3 illustrates a third possible structure of the system according tothe present invention. The structure of the embodiment shown in FIG. 3is similar to that of FIG. 1, except that the phosphor composition 222is coated onto a surface of the envelope 218, instead of being formedover the LED chip 212. The phosphor composition 222 is preferably coatedon the inside surface of the envelope 218, although the phosphor may becoated on the outside surface of the envelope, if desired. The phosphorcomposition 222 may be coated on the entire surface of the envelope, oronly a top portion of the surface of the envelope. The radiation 226emitted by the LED chip 212 mixes with the light emitted by the phosphorcomposition 222, and the mixed light appears as white light 224. Ofcourse, the structures of FIGS. 1-3 may be combined, and the phosphormay be located in any two or all three locations, or in any othersuitable location, such as separately from the envelope, or integratedinto the LED.

In any of the above structures, the lamp may also include a plurality ofscattering particles (not shown), which are embedded in the encapsulantmaterial. The scattering particles may comprise, for example, alumina ortitania. The scattering particles effectively scatter the directionallight emitted from the LED chip, preferably with a negligible amount ofabsorption.

As shown in a fourth structure in FIG. 4, the LED chip 412 may bemounted in a reflective cup 430. The cup 430 may be made from or coatedwith a dielectric material, such as alumina, titania, or otherdielectric powders known in the art, or be coated by a reflective metal,such as aluminum or silver. The remainder of the structure of theembodiment of FIG. 4 is the same as those of any of the previousfigures, and can include two leads 416, a conducting wire 432, and anencapsulant material 420. The reflective cup 430 is supported by thefirst lead 416 and the conducting wire 432 is used to electricallyconnect the LED chip 412 with the second lead 416.

Another structure (particularly for backlight applications) is a surfacemounted device (“SMD”) type light emitting diode 550, e.g. asillustrated in FIG. 5. This SMD is a “side-emitting type” and has alight-emitting window 552 on a protruding portion of a light guidingmember 554. An SMD package may comprise an LED chip as defined above,and a phosphor material that is excited by the light emitted from theLED chip. Other backlight devices include, but are not limited to, TVs,computers, smartphones, tablet computers and other handheld devices thathave a display including a semiconductor light source; and a colorstable Mn⁴⁺ doped phosphor according to the present invention.

When used with an LED emitting at from 350 to 550 nm and one or moreother appropriate phosphors, the resulting lighting system will producea light having a white color. Lamp 10 may also include scatteringparticles (not shown), which are embedded in the encapsulant material.The scattering particles may comprise, for example, alumina or titania.The scattering particles effectively scatter the directional lightemitted from the LED chip, preferably with a negligible amount ofabsorption.

In addition to the color stable Mn⁴⁺ doped phosphor, phosphorcomposition 22 may include one or more other phosphors. When used in alighting apparatus in combination with a blue or near UV LED emittingradiation in the range of about 250 to 550 nm, the resultant lightemitted by the assembly will be a white light. Other phosphors such asgreen, blue, yellow, red, orange, or other color phosphors may be usedin the blend to customize the white color of the resulting light andproduce specific spectral power distributions. Other materials suitablefor use in phosphor composition 22 include electroluminescent polymerssuch as polyfluorenes, preferably poly(9,9-dioctyl fluorene) andcopolymers thereof, such aspoly(9,9′-dioctylfluorene-co-bis-N,N′-(4-butylphenyl)diphenylamine)(F8-TFB); poly(vinylcarbazole) and polyphenylenevinylene and theirderivatives. In addition, the light emitting layer may include a blue,yellow, orange, green or red phosphorescent dye or metal complex, or acombination thereof. Materials suitable for use as the phosphorescentdye include, but are not limited to, tris(1-phenylisoquinoline) iridium(III) (red dye), tris(2-phenylpyridine) iridium (green dye) and Iridium(III) bis(2-(4,6-difluorephenyl)pyridinato-N,C2) (blue dye).Commercially available fluorescent and phosphorescent metal complexesfrom ADS (American Dyes Source, Inc.) may also be used. ADS green dyesinclude ADS060GE, ADS061GE, ADS063GE, and ADS066GE, ADS078GE, andADS090GE. ADS blue dyes include ADS064BE, ADS065BE, and ADS070BE. ADSred dyes include ADS067RE, ADS068RE, ADS069RE, ADS075RE, ADS076RE,ADS067RE, and ADS077RE.

Suitable phosphors for use in phosphor composition 22 in addition to theMn⁴⁺ doped phosphor include, but are not limited to:

((Sr_(1−z)(Ca, Ba, Mg, Zn)_(z))_(1−(x+w))(Li, Na, K,Rb)_(w)Ce_(x))₃(Al_(1−y)Si_(y))O_(4+y+3 (x−w))F_(1−y−3(x−w)), 0<x≦0.10,0≦y≦0.5, 0≦z≦0.5, 0≦w≦x; (Ca, Ce)₃Sc₂Si₃O₁₂(CaSiG);(Sr,Ca,Ba)₃Al_(1-x)Si_(x)O_(4+x)F_(1−x):Ce³⁺ (SASOF));(Ba,Sr,Ca)₅(PO₄)₃(Cl,F,Br,OH):Eu²⁺,Mn²⁺; (Ba,Sr,Ca)BPO₅:Eu²⁺,Mn²⁺;(Sr,Ca)₁₀(PO₄)₆*νB₂O₃:Eu²⁺ (wherein 0<ν≦1); Sr₂Si₃O₈*2SrCl₂:Eu²⁺;(Ca,Sr,Ba)₃MgSi₂O₈:Eu²⁺,Mn²⁺; BaAl₈O₁₃:Eu²⁺;2SrO*0.84P₂O₅*0.16B₂O₃:Eu²⁺; (Ba,Sr,Ca)MgAl₁₀O₁₇:Eu²⁺,Mn²⁺;(Ba,Sr,Ca)Al₂O₄:Eu²⁺; (Y,Gd,Lu,Sc,La)BO₃:Ce³⁺,Tb³⁺; ZnS:Cu⁺,Cl⁻;ZnS:Cu⁺,Al³⁺; ZnS:Ag⁺,Cl⁻; ZnS:Ag⁺,Al³⁺;(Ba,Sr,Ca)₂Si_(1−ξ)O_(4−2ξ):Eu²⁺ (wherein −0.2≦ξ≦0.2);(Ba,Sr,Ca)₂(Mg,Zn)Si₂O₇:Eu²⁺; (Sr,Ca,Ba)(Al,Ga,In)₂S₄:Eu²⁺;(Y,Gd,Tb,La,Sm,Pr,Lu)₃(Al,Ga)_(5−α)O_(12−3/2α):Ce³⁺ (wherein 0≦α≦0.5);(Y,Gd,Lu,Tb)₃(Al,Ga)₅O₁₂:Ce³⁺; (Ca,Sr)₈(Mg,Zn)(SiO₄)₄Cl₂:Eu²⁺,Mn²⁺;Na₂Gd₂B₂O₇:Ce³⁺,Tb³⁺; (Sr,Ca,Ba,Mg,Zn)₂P₂O₇:Eu²⁺,Mn²⁺;(Gd,Y,Lu,La)₂O₃:Eu³⁺,Bi³⁺; (Gd,Y,Lu,La)₂O₂S:Eu³⁺,Bi³⁺;(Gd,Y,Lu,La)VO₄:Eu³⁺,Bi³⁺; (Ca,Sr)S:Eu²⁺,Ce³⁺; SrY₂S₄:Eu²⁺;CaLa₂S₄:Ce³⁺; (Ba,Sr,Ca)MgP₂O₇:Eu²⁺,Mn²⁺; (Y,Lu)₂WO₆:Eu³⁺,Mo⁶⁺;(Ba,Sr,Ca)_(β)Si_(γ)N_(μ):Eu²⁺ (wherein 2β+4γ=3μ;(Ba,Sr,Ca)₂Si_(5−x)Al_(x)N_(8−x)O_(x):Eu²⁺ (wherein 0≦x≦2);Ca₃(SiO₄)Cl₂:Eu²⁺;(Lu,Sc,Y,Tb)_(2−u−v)Ce_(v)Ca_(1+u)Li_(w)Mg_(2−w)P_(w)(Si,Ge)_(3−w)O_(12−u/2)(where −0.5≦u≦1, 0<v≦0.1, and 0≦w≦0.2);(Y,Lu,Gd)_(2−φ)Ca_(φ)Si₄N_(6+φ)C_(1−φ):Ce³⁺, (wherein 0≦φ≦0.5);(Lu,Ca,Li,Mg,Y) α-SiAlON doped with Eu²⁺ and/or Ce³⁺;(Ca,Sr,Ba)SiO₂N₂:Eu²⁺,Ce³⁺; β-SiAlON:Eu²⁺, 3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺;(Sr,Ca,Ba,Mg)AlSiN₃:Eu²⁺; (Sr,Ca,Ba)₃SiO₅:Eu²⁺;Ca_(1−c−f)Ce_(c)Eu_(f)Al_(1+c)Si_(1−c)N₃, (where 0≦c≦0.2, 0≦f≦0.2);Ca_(1−h−r)Ce_(h)Eu_(r)Al_(1−h)(Mg,Zn)_(h)SiN₃, (where 0≦h≦0.2, 0≦r≦0.2);Ca_(1−2s−t)Ce_(s)(Li,Na)_(s)Eu_(t)AlSiN₃, (where 0≦s≦0.2, 0≦f≦0.2,s+t>0); and Ca_(1−σ−χ−φ)Ce_(σ)(Li,Na)_(χ)Eu_(φ)Al_(1+σ−χ)Si_(1−σ+χ)N₃,(where 0≦σ≦0.2, 0≦χ≦0.4, 0≦φ≦0.2).

In particular, phosphor composition 22 may include one or more phosphorsthat result in a green spectral power distribution under ultraviolet,violet, or blue excitation. In the context of the present invention,this is referred to as a green phosphor or green phosphor material. Thegreen phosphor may be a single composition or a blend that emits lightin a green to yellow-green to yellow range, such as cerium-doped yttriumaluminum garnets, more particularly (Y,Gd,Lu,Tb)₃(Al,Ga)₅O₁₂:Ce³⁺. Thegreen phosphor may also be a blend of blue- and red-shifted garnetmaterials. For example, a Ce³⁺-doped garnet having blue shifted emissionmay be used in combination with a Ce³⁺-doped garnet that has red-shiftedemission, resulting in a blend having a green spectral powerdistribution. Blue- and red-shifted garnets are known in the art. Insome embodiments, versus a baseline Y₃Al₅O₁₂:Ce³⁺ phosphor, ablue-shifted garnet may have Lu³⁺ substitution for Y³⁺, Ga³⁺substitution for Al³⁺, or lower Ce³⁺ doping levels in a Y₃Al₅O₁₂:Ce³⁺phosphor composition. A red-shifted garnet may have Gd³⁺/Tb³⁺substitution for Y³⁺ or higher Ce³⁺ doping levels.

The ratio of each of the individual phosphors in the phosphor blend mayvary depending on the characteristics of the desired light output. Therelative proportions of the individual phosphors in the variousembodiment phosphor blends may be adjusted such that when theiremissions are blended and employed in an LED lighting device, there isproduced visible light of predetermined x and y values on the CIEchromaticity diagram. As stated, a white light is preferably produced.This white light may, for instance, may possess an x value in the rangeof about 0.20 to about 0.55, and a y value in the range of about 0.20 toabout 0.55. As stated, however, the exact identity and amounts of eachphosphor in the phosphor composition can be varied according to theneeds of the end user. For example, the material can be used for LEDsintended for liquid crystal display (LCD) backlighting. In thisapplication, the LED color point would be appropriately tuned based uponthe desired white, red, green, and blue colors after passing through anLCD/color filter combination. The list of potential phosphor forblending given here is not meant to be exhaustive and these Mn⁴⁺-dopedphosphors can be blended with various phosphors with different emissionto achieve desired spectral power distributions.

In some embodiments, lighting apparatus 10 has a color temperature lessthan or equal to 4200° K, and phosphor composition 22 includes a redphosphor consisting of a color stable Mn⁴⁺ doped phosphor of formula I.That is, the only red phosphor present in phosphor composition 22 is thecolor stable Mn⁴⁺ doped phosphor; in particular, the phosphor isK₂SiF₆:Mn⁴⁺. The composition may additionally include a green phosphor.The green phosphor may be a Ce³⁺-doped garnet or blend of garnets,particularly a Ce³⁺-doped yttrium aluminum garnet, and moreparticularly, YAG having the formula (Y,Gd,Lu,Tb)₃(Al,Ga)₅O₁₂:Ce³⁺. Whenthe red phosphor is K₂SiF₆:Mn⁴⁺, the mass ratio of the red phosphor tothe green phosphor material may be less than 3.3, which may besignificantly lower than for red phosphors of similar composition, buthaving lower levels of the Mn dopant.

LED devices incorporating the color stable phosphors and used forbacklighting or general illumination lighting may have a color shift of<1.5 MacAdam ellipses over 2,000 hours of device operation, and, inparticular embodiments, <1 MacAdam ellipse over 2,000 hours, where thephosphor/polymer composite is in direct contact with the LED chipsurface, LED wall plug efficiency greater than 40%, and LED currentdensities are greater than 2 A/cm². In accelerated testing, where thephosphor/polymer composite is in direct contact with the LED chipsurface, LED wall plug efficiency greater than 18%, and LED currentdensities are greater than 70 A/cm², LED devices may have color shift of<1.5 MacAdam ellipse over 30 minutes.

The color stable Mn⁴⁺ doped phosphors of the present invention may beused in applications other than those described above. For example, thematerial may be used as a phosphor in a fluorescent lamp, in a cathoderay tube, in a plasma display device or in a liquid crystal display(LCD). The material may also be used as a scintillator in anelectromagnetic calorimeter, in a gamma ray camera, in a computedtomography scanner or in a laser. These uses are merely exemplary andnot limiting.

EXAMPLES General Procedures

Silicone Tape Sample Preparation

Samples were prepared by mixing 500 mg of the material to be tested with1.50 g silicone (Sylgard 184). The mixture was degassed in a vacuumchamber for about 15 minutes. The mixture (0.70 g) was poured into adisc-shaped template (28.7 mm diameter and 0.79 mm thick) and baked for30 minutes at 90° C. The sample was cut into squares of sizeapproximately 5 mm×5 mm for testing.

Stability Testing

High Light Flux Conditions

A laser diode emitting at 446 nm was coupled to an optical fiber with acollimator at its other end. The power output was 310 mW and the beamdiameter at the sample was 700 microns. This is equivalent to a flux of80 W/cm² on the sample surface. The spectral power distribution (SPD)spectrum that is a combination of the scattered radiation from the laserand the emission from the excited phosphor is collected with a 1 meter(diameter) integrating sphere and the data processed with thespectrometer software (Specwin). At intervals of two minutes, theintegrated power from the laser and the phosphor emission were recordedover a period of about 21 hours by integrating the SPD from 400 nm to500 nm and 550 nm to 700 nm respectively. The first 90 minutes of themeasurement are discarded to avoid effects due to the thermalstabilization of the laser. The percentage of intensity loss due tolaser damage is calculated as follows:

${{Intensity}\mspace{14mu}{loss}\mspace{14mu}(\%)} = {100\frac{\left( {{Power} - {{Initial}\mspace{14mu}{power}}} \right)}{{Initial}\mspace{14mu}{power}}}$While only the emitter power from the phosphor is plotted, theintegrated power from the laser emission as well as its peak positionwas monitored to ensure that the laser remained stable (variations ofless than 1%) during the experiment.High Temperature High Humidity (HHTH) Treatment

Samples for high temperature, high humidity (HTHH) treatment were madeby mixing phosphor powders into a two-part methyl silicone binder(RTV-615, Momentive Performance Materials) in a ratio of 0.9 g phosphorto 0.825 g silicone (parts A+B). The phosphor/silicone mixture is thenpoured into aluminum sample holders and cured at 90° C. for 20 minutes.Control samples were stored under nitrogen, and samples for exposure toHTHH conditions were placed into a 85° C./85% RH controlled atmospherechamber. These HTHH samples are periodically removed and theirluminescence intensity under 450 nm excitation compared to that of thecontrol samples.

Relative Brightness

A phosphor tape containing 25 wt % phosphor, 1¼″ wide and 1/32″ thick,is prepared according to the procedure above. The tape is placed withinan integrating sphere about ½ ″ away from the LED and held in place by acylindrical spacer coated with a highly reflective film. Emissionintensity was measured at wavelengths ranging between 550 nm and 700 nm,integrated and normalized to emission of a reference sample composed ofa commercial K₂SiF₆:Mn⁴⁺ material containing 0.7 weight % Mn, obtainedfrom ShinEtsu Chemicals.

Examples 1-4 Preparation of K₂SiF₆:Mn⁴⁺ with Manganese Levels Rangingfrom 0.91 wt % to 1.19 wt %

Amounts and distribution of starting materials among Beakers A-D areshown in Table 1. For Example 4, 5 mL of acetone was also added tobeaker B. Procedure: Beaker A was stirred aggressively, and the contentsof beaker B were added dropwise at a rate of 75 mL/min for 30 secondsand then 60 mL/min for the remainder of the reaction. The contents ofbeaker D were added dropwise to beaker A at a rate of 13 mL/minute 20seconds after the contents of beaker B began to be added. The contentsof beaker C were added dropwise to beaker A at a rate of 13 mL/minute 30seconds after the contents of beaker B began to be added. Theprecipitate was digested for 5 minutes and the stirring was stopped. Thesupernatant was decanted, and the precipitate was vacuum filtered,rinsed once with acetic acid and twice with acetone, and then driedunder vacuum. The dried powder was sifted through 44 micron mesh, andannealed under 20% F₂ for 8 hr. at 540° C. The annealed phosphor waswashed in a solution of 49% HF saturated with K₂SiF₆, dried under vacuumand sifted.

The amount of manganese incorporated in the phosphor was determined byinductively coupled plasma mass spectrometry (ICP-MS), and is reportedas weight %, based on total weight of the phosphor material.

TABLE 1 Source KF (g) K₂MnF₆ (g) 35% H₂SiF₆ (mL) 49% HF (mL) Example 1:0.91% Mn Beaker A 19 g 1.19 100 Beaker B 47.3 150 Beaker C 1.45 25Beaker D 8.9 20 Example 2: 1.19% Mn Beaker A 19 0.88 90 Beaker B 46.8148 Beaker C 2.04 35 Beaker D 8.9 20 Example 3: 1.17% Mn Beaker A 140.88 85 Beaker B 46.6 147 Beaker C 2.0  30 Beaker D 14 28 Example 4:0.94% Mn Beaker A 10 0.88 80 Beaker B 46.6 147 Beaker C 2.0  30 Beaker D14 28

Samples were evaluated for laser damage, quantum efficiency (reported asrelative QE, setting the value of QE of a reference material composed ofcommercial K₂SiF₆:Mn⁴⁺ containing 0.7 weight % Mn, obtained fromShinEtsu Chemicals, to 100%) and absorbance at 450 nm. Results are shownin Table 2. It can be seen that laser damage was lower, and QE andabsorbance were higher compared to the commercial control.

TABLE 2 Example No. Laser Damage QE (relative) Abs 450 nm wt % MnControl 7.2% 100.0% 68.8% 0.73% 1 1.0% 103.0% 74.0% 0.91% 2 2.7% 103.6%80.1% 1.19% 3 1.3% 101.6% 75.3% 1.17% 4 1.5% 103.3% 73.0% 0.94%

Comparative Example 1

Mn-doped potassium fluorosilicate, containing 0.84 wt % Mn, based ontotal weight of the material, was annealed I a furnace at 540° C. underan atmosphere containing 20% F₂/80% N₂ at 10 psia for 8 hours. Theannealed phosphor was washed in a solution of 49% HF saturated withK₂SiF₆, dried under vacuum and sifted. The phosphor and an annealed,untreated commercial sample were tested under conditions of high lightflux. Results are shown in Table 3.

TABLE 3 Example Laser Relative No. Damage QE, % % Mn Conditions Control10.9% 100 0.84% No treatment Comp. 1.5% 107.5 0.82% 540° C., 20% F₂/80%Ex. 1 N₂, 10 psia, 8 hours

Examples 5 and 6 Properties of K₂SiF₆:Mn⁴⁺ with 0.9 wt % and 1.25 wt %Manganese

Mn-doped potassium fluorosilicate materials were prepared and treated asin Examples 1-4. Quantum efficiency and decay time were measured andweight % Mn was determined by ICP-MS, before and after treatment.Results are shown in Table 4. It can be seen that the quantum efficiencyof high Mn samples was improved, and the onset/effects of concentrationquenching were reduced. The improvement in QE at least is significantlygreater than that observed at lower Mn levels. For example, QE of thephosphor of Comparative Example 1, having 0.84 wt % Mn, increased from100 (relative) to 107 (relative), about 7% increase, while the increaseshown in Table 4 is about 15% for the sample containing 0.9 wt % Mn, andabout 20% for the sample containing 1.25 wt % Mn.

TABLE 4 Example QE Decay Mn level No. (relative) time (wt %) Notes 5 908.19 ms 0.94% Before treatment 104.5 8.70 ms 0.90% After treatment 6 807.95 ms 1.39% Before treatment 103 8.69 ms 1.25% After treatment

Comparative Example 2

A commercial K₂SiF₆:Mn⁴⁺ phosphor with a manganese content of 0.70% (asdetermined by Induced Coupled Plasma) was placed in a furnace under anitrogen (80%) and fluorine (20%) atmosphere at 10 psia and heated at540° C. for 8 hours. After 8 hours, the temperature was decreased at arate of 10° C. per minute. The annealed phosphor was washed in asolution of 49% HF saturated with K₂SiF₆, dried under vacuum and sifted.

Example 7 Slow Cooling after Annealing

A commercial K₂SiF₆:Mn⁴⁺ phosphor with a manganese content of 0.70% (asdetermined by Induced Coupled Plasma) was placed in furnace under anitrogen (80%) and fluorine (20%) atmosphere at 10 psia and heated at540° C. for 8 hours. After 8 hours, the temperature was decreased at arate of 1° C. per minute. The annealed phosphor was washed in a solutionof 49% HF saturated with K₂SiF₆, dried under vacuum and sifted.

Stability of the phosphors of Comparative Example 2 and Example 7 wasevaluated and compared to the untreated commercial control havingmanganese content of 0.70%. Annealing improved stability, and using aslow cool down further decreased % intensity loss.

Examples 8-23 K₂SiF₆:Mn⁴⁺ with Manganese Levels Ranging from 1.1 wt % to5.3 wt % Comparative Examples 3-5 K₂SiF₆:Mn⁴⁺ with Manganese LevelsRanging from 0.52 wt % to 0.79 wt %

Mn-doped potassium fluorosilicate materials were prepared and posttreated as in Examples 1-4, except that the amounts of raw materialswere adjusted according to the higher levels of manganese. Relativequantum efficiency, emission decay lifetime and brightness were measuredfor the products before and after the post treatment. Results are shownin Table 5.

TABLE 5 Before After Comp. Relative Relative Relative Relative Ex. Ex.[Mn⁴⁺], QE, Brightness, Lifetime, QE, Brightness, Lifetime, No. No. wt %% % ms % % ms 1 0.52 92 88 104 95 8.6 2 0.7 98 8.4 106 110 8.6 3 0.79 97106 8.4 106 117 8.6 8 1.1 103 134 8.6 9 1.4 89 122 8.0 104 140 8.6 102.1 83 124 7.7 102 151 8.5 11 2.6 69 108 7.2 101 154 8.5 12 2.7 76 12398 156 8.5 13 2.9 65 105 7.2 97 158 8.5 14 3.0 72 110 7.1 105 163 8.4 153.2 59 93 7.3 89 137 8.2 16 3.4 60 95 6.8 98 155 8.4 17 3.4 51 85 6.8 95153 8.4 18 3.5 53 85 6.9 91 143 8.3 19 3.6 53 87 7.0 88 141 8.2 20 3.930 53 6.3 67 116 7.8 21 4.0 42 69 6.7 82 135 8.1 22 4.4 17 29 7.9 36 616.8 23 5.3 7 11 4.3 31 53 7.0

Untreated samples had a relative QE lower than 90% at Mn⁴⁺concentrations over 1% due to concentration quenching. The range atwhich the QE remained high was extended to at least 3 wt % by posttreatment, and lifetime was greater than 8.4 ms to about 3.4 wt %. Thesignificant improvement in properties resulting from the post treatmentextended to about 4 wt %.

Example 24 K₂SiF₆:Mn⁴⁺ Blends with Color Temperature of 3000° K

The Mn-doped potassium fluorosilicate materials of Examples 2, 3 and 10were blended with YAG and tapes were prepared to emit light having acolor temperature of 3000° K. Composition of the blends is shown inTable 6.

TABLE 6 Red phosphor Blend Example [Mn⁴⁺], Composition YAG, Silicone,No. wt % Wt, % % wt. % wt. 2 0.70% 20.8% 5.2% 74.0% 3 0.79% 18.6% 5.4%76.0% 10 2.05% 8.4% 6.0% 85.6%

It can be seen that significantly less of the red phosphor material withhigher Mn concentration was used, compared to the materials having lowerMn concentration.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

The invention claimed is:
 1. A process for synthesizing a color stableMn⁴⁺ doped phosphor, the process comprising contacting a precursor offormula I,

at an elevated temperature with a fluorine-containing oxidizing agent ingaseous form to form the color stable Mn⁴⁺ doped phosphor; wherein A isLi, Na, K, Rb, Cs, or a combination thereof; M is Si, Ge, Sn, Ti, Zr,Al, Ga, In, Sc, Hf, Y, La, Nb, Ta, Bi, Gd, or a combination thereof; xis 1, 2, or 3, and is equal to the absolute value of the charge of the[MF_(y)] ion; y is 5, 6 or 7; and an amount of Mn ranges from about 0.5wt % to about 4 wt %, based on total weight.
 2. A process according toclaim 1, wherein the amount of Mn ranges from about 0.9 wt % to about 4wt %.
 3. A process according to claim 1, wherein the amount of Mn rangesfrom about 0.9 wt % to about 3.4 wt %.
 4. A process according to claim1, wherein the amount of Mn ranges from about 0.9 wt % to about 3.0 wt%.
 5. A process according to claim 1, wherein the color stable Mn⁴⁺doped phosphor is K₂SiF₆:Mn⁴⁺ and the amount of Mn ranges from about 0.5wt % to about 4 wt %, based on total weight.
 6. A process according toclaim 1, wherein the temperature is any temperature in a range fromabout 500° C. to about 600° C.
 7. A process according to claim 1,wherein the fluorine-containing oxidizing agent is F₂.